JPH1168702A - Optical signal transmission method and its system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the number of optical signals sent simultaneously by transmitting the optical signals while adjusting polarized wave planes in orthogonal directions to each other. SOLUTION: Optical signals outputted from plural light sources 11, 21 are coupled by a photocoupler 6, the coupled signal is sent through an optical fiber 5 and received by a center station 1, where the signal is demodulated in the optical signal transmission method. In terminal stations 10, 20, polarized wave adjustment devices 13, 23 adjust the optical signal from each light source so as to be linearly polarized and the polarized planes are orthogonal to each other and the center station side uses a polarized wave adjustment device 2 to adjust the polarized plane of the optical signal from the optical fiber to be a state equivalent to the polarized plane adjusted at the terminal station side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to optical CATV and optical I
The present invention relates to an optical signal transmission used for a TV or the like, and more particularly, to an optical signal transmission method and apparatus for linearly polarizing a polarization plane of an optical signal for transmission.

[0002]

[Related Background Art] Conventionally, in this type of optical signal transmission,
Optical signals output from a plurality of light sources are combined by an optical coupler and transmitted to a single optical fiber, and the optical signal is received by a photodetector including one photodiode (PD).
In addition, there is one that demodulates with a demodulator. in this way,
When a plurality of optical signals are received by one PD, optical beat noise has been generated at a frequency corresponding to the wavelength difference between the optical signals. For this reason, the emission wavelength of the light source (hereinafter simply referred to as “wavelength”)
) Was incorporated into the system without selection,
The wavelength difference between the wavelengths of adjacent light sources is narrow, and optical beat noise may be generated in a relatively low frequency band, for example, a transmission band, and the transmission quality may be degraded due to the influence.

Therefore, in the conventional system, the wavelength of the beat noise becomes higher than a desired frequency, and the wavelengths of the light sources are selected so that the wavelengths between the light sources are arranged so that the deterioration of the transmission quality is minimized.

[0004]

However, in the above system, the number of optical signals that can be transmitted simultaneously in a fixed transmission band is determined in consideration of the wavelength difference between the optical signals. Therefore, in order to maximize the number of optical signals, it is necessary to arrange the wavelengths between the optical signals at the shortest wavelength interval based on the wavelength difference.

The level of the optical beat noise depends on the coupling angle between the polarization planes of the two optical signals involved in the beat generation. In the conventional system, each optical signal is adjusted without adjusting the coupling angle. The signals were combined and transmitted. The present invention has been made in view of the above circumstances, and provides an optical signal transmission method and apparatus capable of adjusting the polarization plane of an optical signal in a direction orthogonal to the optical signal, transmitting the signal, and increasing the number of optical signals that can be transmitted simultaneously. Aim.

It is another object of the present invention to provide an optical signal transmission method and apparatus capable of receiving an optical signal without generating optical beat noise. It is another object of the present invention to provide an optical signal transmission method and apparatus capable of adjusting the plane of polarization of an optical signal according to the state of the plane of polarization of the optical signal that changes. It is a further object of the present invention to provide an optical signal transmission method and apparatus capable of adjusting the polarization plane of an optical signal according to the level of optical beat noise.

[0007]

In order to achieve the above object, according to the present invention, optical signals output from the light sources of a plurality of transmitters are coupled to, for example, optical couplers and transmitted to an optical transmission line composed of optical fibers. An optical signal transmission device for receiving the optical signal with a PD of a light receiving unit and demodulating the optical signal includes a polarization adjuster for adjusting the plane of polarization of the optical signal from the light source to linearly polarized light and adjusting the polarization plane to be orthogonal to each other. An optical signal transmission device including a first polarization adjusting unit is provided.

That is, optical signals of the same or adjacent emission wavelengths are linearly polarized by a first polarization adjuster, adjusted so as to be orthogonal to each other, and then coupled by an optical coupler. By receiving the combined optical signal by the PD via the optical fiber, the level of the optical beat noise generated by the influence of the optical signal is set to “0”.

Further, according to the present invention, the first polarization adjuster comprises:
When there are at least three optical signals, the emission wavelengths are the same or adjacent two optical signals as a set, and the polarization planes of the optical signals in each set are linearly polarized, and orthogonal to each other, It is preferable that the light source sets a wavelength interval between the set of optical signals and another set or one of the optical signals whose wavelengths are adjacent to the set of optical signals at a predetermined interval and outputs the set.

Further, according to the present invention, the light receiving section is provided with a second polarization adjusting means comprising a polarization adjuster for adjusting the polarization plane of the input optical signal to linearly polarized light and adjusting the polarization plane to be orthogonal to each other. It is preferable to adjust the polarization plane of the optical signal before receiving the light. Further, according to the present invention, a first measuring means comprising a polarization analyzer for measuring a state of a polarization plane of an optical signal output to an optical fiber, and the polarization plane by a first polarization analyzer according to the measurement result. A first control means for controlling the adjustment of the optical signal, a second measuring means comprising a polarization analyzer for measuring the state of the plane of polarization of the optical signal input from the optical fiber, and Controlling the adjustment of the polarization plane by the second polarization analyzer in accordance with the fourth
It is preferable that the control unit is provided on the light receiving unit side and the transmitting unit and the light receiving unit automatically adjust the polarization plane of the optical signal.

Further, according to the present invention, there is provided a detecting means comprising a noise detecting device for detecting optical beat noise generated at the time of receiving an optical signal, and adjusting the polarization plane by a polarization analyzer according to the detected noise level. It is preferable that a fifth control means for controlling the optical signal is provided on the light receiving unit side, and the light receiving unit automatically adjusts the polarization plane of the optical signal according to the level of the optical beat noise. Further, in the present invention, a wavelength setting means for setting an emission wavelength of the optical signal, and the first polarization adjuster based on a relationship between a coupling angle of a polarization plane of each optical signal and a noise level of beat noise. A second control means for controlling the adjustment of the polarization plane by the above, and setting the polarization plane to an arbitrary state; and setting the emission wavelength by the wavelength setting means based on the relationship between the noise level of the beat noise and the wavelength interval. And a third control means for controlling the emission wavelength to an arbitrary interval, arbitrarily controlling the adjustment of the polarization plane of the optical signal and the setting of the emission wavelength to set the level of the optical beat noise to “0”. It is also preferable to do so.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical signal transmission method and apparatus according to the present invention will be described with reference to FIGS. FIG. 1 is a block diagram showing a first embodiment of a system configuration using the optical signal transmission method according to the present invention. In the figure,
In the above system, a plurality of, for example, two terminal stations 10, 20
And the center station 1 are connected via an optical fiber 5.

The terminal stations 10 and 20 include a polarization adjuster 1.
3 and 23, respectively, and the polarization adjusters 13 and 2
3 are connected to the optical fiber 5 via the optical coupler 6 such that the optical signals of the terminal stations 10 and 20 output from the optical fiber 3 are combined and output to the optical fiber 5. Each terminal station 10,
Reference numeral 20 denotes light sources 11 and 21 which are connected to the polarization adjusters 13 and 23 and are composed of, for example, laser diodes (LD), and LDs.
Modulators 12 and 22 for modulating optical signals output from the optical modulators 11 and 21 are provided.

The center station 1 has a polarization adjuster 2 connected to an optical fiber 5, a light receiver 3 composed of, for example, a PD for receiving the optical signal whose polarization has been adjusted by the polarization adjuster 2, and And a demodulator 4 for demodulating an optical signal. By the way, it is known that the level of the optical beat noise depends on the coupling angle of the polarization plane of the two optical signals involved in the beat generation. FIG. 2 is a relationship diagram showing the relationship between the coupling angle (hereinafter, referred to as “polarization angle”) of the polarization planes of the two optical signals and the beat level (normalized beat voltage). In FIG. 2, the solid line is an actual measurement value, the dotted line indicates a theoretical value, and the normalized beat voltage of the beat noise sets the peak value when the polarization angle is 0 degree to “1”. It is a value corresponding to each polarization angle at the time.

In FIG. 2, the difference between the polarization angles of the two optical signals is zero.
In the case of degree, the normalized beat voltage of beat noise is “1”
In the case of ± 90 degrees, the normalized beat voltage is as low as “0”. This is represented by the following equation. For example, E0 · sin (ω0 · t) and E1 · sin (ω1 · t)
Two light considering the case to be received by the PD of the electrical components of the ^{PD, E0 2/2 + E1 2} /2 + E0E1 · cosθcos (ω0-
.omega.1) t where .theta .: an angle at which the polarization planes of both optical signals cross each other. The third term at this time corresponds to an optical beat.

As can be seen from this equation, the level of the optical beat changes in proportion to θ, and increases as θ approaches 0 degrees, and decreases as θ approaches ± 90 degrees. Therefore, in the polarization adjusters 13 and 23 of this embodiment, the LDs 11 and
The polarization planes of both optical signals output from 21 become linearly polarized near the exit of the optical coupler 6 and are orthogonal to each other (90 degrees).
Adjust to In the polarization adjuster 2, the polarization plane of the optical signal input from the optical fiber 5 is changed by the polarization adjuster 1.
The state is adjusted to the state at the time of adjustment by 3, 3, that is, a state of linearly polarized light and orthogonal to each other.

That is, in the terminal stations 10 and 20, the two optical signals output from the LDs 11 and 21 modulated by the modulators 12 and 22 are linearly polarized by the polarization adjusters 13 and 23, and mutually polarized. It is output orthogonally. Each optical signal is coupled by the optical coupler 6, input to one optical fiber, and output to the center station 1. In the optical signal output to the optical fiber 5, the state of the polarization plane may fluctuate from the state adjusted on the terminal station side due to weather conditions, environmental conditions (for example, vibration or temperature change of the optical fiber) or the like. is there. However, since the relationship between the polarization planes of the simultaneously transmitted optical signals is maintained during the same propagation process, the polarization fluctuation can be returned to the original state at the center station.

Therefore, in the center station 1, the polarization adjuster 2 again adjusts the plane of polarization of the optical signal input from the optical fiber 5 so that the plane of polarization is linearly polarized and orthogonal to each other. The optical signal thus adjusted is received by one PD 3 and demodulated by the demodulator 4. Thus, in this embodiment, a polarization adjuster is provided on each terminal station side and the center station, and the polarization planes of the optical signals are linearly polarized and combined with each other in a state of being orthogonal to each other and transmitted. Since the relationship is returned to the original state (in the state of linearly polarized light and orthogonal to each other), light is received by one light receiver.
There is no need to consider the interval between the wavelengths λ1 and λ2 of each optical signal,
Even if the wavelengths λ1 and λ2 are the same, the level of the optical beat noise generated by the influence of the optical signal becomes “0”,
The number of optical signals that can be transmitted can be increased.

Next, a second embodiment of the system configuration when three or more optical signals exist will be described with reference to the block diagram of FIG. In the second embodiment of FIG. 3 and the subsequent embodiments, the same components as those in FIG. 1 are denoted by the same reference numerals for convenience of explanation. In the system of FIG. 3, in addition to the configuration of FIG. 1, three or more terminal stations N0 are connected to the optical coupler 6 via the polarization adjuster N3. Here, N is any positive number.

In this system, for example, the terminal stations 10, 2
0 and other terminal stations and terminal stations N0 (not shown), each of which constitutes a pair. The polarization adjuster is arranged such that the polarization plane of the optical signal for each pair is linear near the exit of the optical coupler 6. The polarization is adjusted so as to be orthogonal to each other. For this reason, the optical signals from each set of LDs may have the same wavelength or be adjacent to each other, but the other set or one set of adjacent sets of wavelengths (when the number of terminal stations in the system is an odd number) is adjacent to the set. It is necessary to set the wavelength interval between the optical signal and the optical signal to a predetermined interval (shortest wavelength interval) that can prevent deterioration of transmission quality due to occurrence of an optical beat in a transmission band. The shortest wavelength interval is, as shown in Japanese Patent Application Laid-Open No. Hei 7-231300 previously filed by the present applicant,
-13 to RIN (Relative Intensity Noise) value
It is desirable that the light emission wavelengths of the two adjacent sets of terminal stations have an interval of 0.2 nm so that a noise value of about 0 dB / Hz is generated.

That is, when the upstream transmission of the optical signal of this embodiment is performed at a wavelength of, for example, 1.55 μm, the wavelengths λ1, λ2 of the terminal stations 10, 20 are set to 1550.0 nm, for example, the wavelengths λ1, λ2. And the wavelength λ of an adjacent terminal station (not shown)
3, λ4 is set to 1550.2 nm, and the wavelength λN of the terminal station N0 is set to 1550. Set to Nnm. Thus, in the present embodiment, in the same set of terminal stations, the polarization planes of the optical signals are combined in a state of being linearly polarized and orthogonal to each other, and in different sets of terminal stations, the wavelengths of the optical signals are different. Are transmitted at predetermined intervals, and their mutual relationship is determined in the same manner as in the first embodiment.
Since the light is received by one optical receiver after returning to the original state at the center station, the level of the optical beat noise generated by the different sets of optical signals is determined only by considering the wavelength interval of the optical signals of the adjacent sets. Can be reduced to a level that does not affect optical signal transmission or can be set to "0", and the number of optical signals that can be transmitted can be increased at most twice.

In these embodiments, it is assumed that an optical signal of video information having a wide exclusive bandwidth is transmitted, and the level of optical beat noise affecting the signal transmission band is set to "0".
However, in the case of information such as a still image, a voice, a character, or the like, which has a narrow exclusive bandwidth, the level of noise jumping into the signal transmission band is small. Therefore, in this case, even if the normalized beat voltage shown in FIG. 2 is about “0.1”, it can sufficiently withstand optical signal transmission. The transmission quality of an optical signal can be improved.

Therefore, in the polarization adjuster according to the present invention, the polarization plane of the optical signal is not limited to that of the embodiment, but may be -85 degrees to -9 degrees.
It is possible to use one that adjusts to 0 degrees or a range of 85 degrees to 90 degrees. In this case, an inexpensive polarization adjuster can be used instead of an expensive polarization adjuster with high adjustment accuracy, and the manufacturing cost can be reduced. In addition, a polarization maintaining fiber can be used for the optical fiber which is one of the components of the system according to the present invention. In this system, the polarization plane of the optical signal is in a predetermined state in the fiber. That is, the linearly polarized light set by the polarization plane adjuster on the terminal station side is received by the PD of the center station while maintaining a state orthogonal to each other.
Since no beat is generated as shown in (1), in the center station, the PD can directly receive the optical signal from the optical fiber, and the polarization adjuster becomes unnecessary.

Further, each of the polarization adjusters 2 and 1 of these embodiments
The adjustment of 3, 23 to N3 may be performed, for example, manually by an operator at the time of installing the system, or automatically adjusted and controlled at the time of installing or using the system as in an embodiment described later. In addition, each of the polarization adjusters 2, 13, 23 to
N3 can be incorporated in each station, or in the case of a system already installed, it can be provided outside the station and connected to each station.

FIG. 4 is a block diagram showing a third embodiment of a system configuration for automatically adjusting the plane of polarization using a polarization analyzer. In this system, an optical coupler 6 is provided on the terminal station side.
A splitter 30 for splitting an optical signal near the exit of the optical amplifier, a polarization analyzer 31 for taking in the split optical signal and measuring the polarization state, and a polarization adjuster 13 according to the measured polarization state. , 23 for controlling the polarization plane by disposing the control device 32 on the terminal station side, and a splitter 40 for splitting the optical signal output from the polarization adjuster 2; The center station side includes a polarization analyzer 41 that takes in a signal and measures a polarization state, and a control device 42 that controls the polarization adjuster 2 to adjust the polarization plane according to the measured polarization state. Has been placed.

In the present embodiment, for example, at the time of initial setting of system installation, the polarization analyzer 31 on the terminal station side measures the state of the polarization plane of each optical signal from each of the terminal stations 10 and 20 and controls the controller 32 And the control device 32 outputs
The operation of each of the polarization adjusters 13 and 23 is controlled in accordance with these measured values so that the polarization planes of the optical signals are linearly polarized and orthogonal to each other.

The polarization analyzer 41 on the center station side takes in one of the optical signals branched via the polarization adjuster 2, measures the state of its polarization plane, and outputs it to the control device 42. The control device 42 controls the operation of the polarization adjuster 2 according to the measured value, and adjusts the polarization plane of the optical signal so as to restore the polarization fluctuation generated during transmission. Since the relationship between the polarization planes of the optical signals transmitted at the same time is maintained in the same propagation process as described above, the polarization fluctuation is adjusted here by adjusting the polarization plane of one optical signal. Can be undone.

Accordingly, in the present embodiment, the optical signal automatically adjusted so that the plane of polarization is linearly polarized light and orthogonal to each other is automatically returned to the above state at the center station side and received. Even if the polarization plane fluctuates during transmission of an optical signal through an optical fiber, the combined optical signal can be received without generating an optical beat. In the present embodiment, for example, even when a new terminal station is added during use of the system, the optical signal from the new terminal station is orthogonal to the optical signal from another terminal station on the terminal station side. Such automatic adjustment makes it possible to use the existing system.

FIG. 5 is a block diagram showing a fourth embodiment of a system configuration for automatically adjusting the plane of polarization using a noise detection device. In this system, the configuration on the terminal station side is the third
This is the same as the embodiment, except that the noise detecting device 43 detects the noise level of the optical beat generated from the optical receiver 3 at the center station side.
And a control device 44 for controlling the polarization adjuster 2 in accordance with the detected noise level to adjust the polarization plane.

In the present embodiment, similarly to the third embodiment, the optical signal from the terminal station is adjusted and output so that the plane of polarization is linearly polarized and orthogonal to each other. In the optical receiver 3 on the center station side, an optical beat may occur in the received signal component due to the fluctuation of the polarization plane during the transmission of the optical signal via the optical fiber 5. Noise detection device 43
Detects the noise level of this optical beat and
The control device 44 controls the operation of the polarization adjuster 2 so that the noise level becomes “0”, and restores the polarization fluctuation generated during the transmission to the original. Adjust the polarization plane of the signal.

Therefore, in the present embodiment, the optical signal automatically adjusted so as to be in the orthogonal state is changed to the above state again so that the noise level of the optical beat detected by the center station becomes "0". Since the automatic adjustment is performed, the optical beat generated due to the change in the polarization plane is eliminated, and the combined optical signal can be received. In the third and fourth embodiments, the case where there are two optical signals has been described. However, the present invention is not limited to this, and the present invention can be similarly used when there are three or more optical signals. In this case, similarly to the second embodiment, it is necessary to set the wavelength interval between the set and another set or an optical signal whose wavelength is adjacent to the shortest wavelength interval.

In the above embodiment, the case where the polarization angles of the optical signals are adjusted to be orthogonal to each other has been described. However, for example, the occurrence of an optical beat can be prevented from the relationship between the polarization angle and the wavelength interval. It is possible. For example, the relationship between the RIN value and the wavelength interval at each beat level (normalized beat voltage) is as shown in FIG. In FIG. 6, when the peak value of the normalized beat voltage is “1”, the RIN value for the wavelength interval is in the worst state,
As the peak value approaches “0”, the RIN value for the wavelength interval is improved. Here, the case where the modulation degree of the optical signal is 90% is shown.

In the case of this relationship, the beat noise is
It is preferred to obtain the above RIN value of -130 dB / Hz. Therefore, from the relationship shown in FIG.
FIG. 7 shows the relationship between the normalized beat voltage and the wavelength interval for obtaining a noise value of dB / Hz. That is, in FIG. 7, for example, when the normalized beat voltage is “1”, the wavelength interval is about 0.2 nm, and when the normalized beat voltage is “0.5”, the wavelength interval is 0.18.
When the normalized beat voltage is “0.1”, the wavelength interval is about 0.13 nm.

Therefore, based on the relationship between FIG. 2 and FIG.
The relationship between the polarization angle and the wavelength interval with respect to the normalized beat voltage can be obtained, and the occurrence of an optical beat can be prevented from the above relationship. FIG. 8 is a block diagram showing a fifth embodiment of the system configuration for automatically adjusting the polarization angle and the wavelength interval based on the relationship between FIG. 2 and FIG. In FIG. 8, the same components as those in the second embodiment of FIG. 3 are denoted by the same reference numerals for convenience of explanation.

Referring to FIG. 8, the control device 33
And the relationship between the polarization angle, the normalized beat voltage, and the normalized beat voltage and the wavelength interval shown in FIG. 7 are stored in a table format, for example. Then, the control device 33 controls the polarization adjuster 1
3, 23 to N3 are controlled to adjust the polarization plane of each optical signal to a predetermined state.
The emission wavelengths of 1 to N1 are controlled so that the wavelength of each optical signal is set to a predetermined wavelength.

For example, when setting the polarization angle of the optical signal to 60 degrees, the control device 33 controls each polarization adjuster based on the table in its own device to adjust the polarization angle. At the same time, the LD of each terminal station is controlled so that the emission wavelength interval between adjacent terminal stations is set to 0.18 nm. On the other hand, when setting the wavelength interval to, for example, 0.13 nm, the control device 33 controls each LD to set the wavelength interval based on the table in the own device, and sets each polarization adjustment. And the optical signal from the same set of terminal stations is adjusted so that the polarization angle becomes 85 degrees.

Therefore, in the present embodiment, the polarization angle and the wavelength interval can be arbitrarily adjusted from the relationship between the polarization angle and the wavelength interval. For example, the polarization angle and the wavelength interval can be adjusted according to the number of terminal stations in the system. Angle and wavelength spacing can be set,
From this relationship, the occurrence of an optical beat can be prevented.
In this embodiment, as in the third and fourth embodiments of FIGS. 4 and 5, a polarization analyzer is provided on the terminal station side to measure the state of the polarization plane of the optical signal, and the measured value is used as the measured value. It is also possible to automatically adjust the polarization plane based on this, or to install a polarization analyzer on the center station side to measure the state of the polarization plane of the optical signal and automatically adjust the polarization plane based on the measured value It is also possible.

Further, in this embodiment, without using a control device, an operator artificially adjusts the polarization of each optical signal based on the relationship between the polarization angle and the normalized beat voltage and between the normalized beat voltage and the wavelength interval. The wave angle and the wavelength may be set. Furthermore, in this embodiment, the case of linearly polarized light has been described. However, the present invention is not limited to this, and can be applied to, for example, a combination with elliptically polarized light. Also, in this case, it is possible to use it together with the setting of the wavelength interval of the optical signal.

[0039]

As described above, according to the present invention, optical signals transmitted from a plurality of light sources are combined and transmitted to an optical transmission line, and the optical signals are received by a light receiving section and demodulated. In the apparatus, the polarization plane of the optical signal from the light source is linearly polarized, and the first polarization control means for adjusting in the direction orthogonal to each other, it is not necessary to consider the wavelength interval of each optical signal, The number of optical signals that can be transmitted simultaneously can be increased.

Further, in the present invention, when at least three optical signals are present, the first polarization adjusting means sets two optical signals having the same wavelength or adjacent wavelengths as a set, and The polarization plane of the optical signal is linearly polarized and orthogonal to each other, and the light source is a wavelength interval between the set of optical signals and another set or one of the optical signals whose wavelengths are adjacent to the set of optical signals. Is output at a predetermined interval.
It is only necessary to consider the wavelength intervals of optical signals in different sets without considering the wavelength intervals of optical signals in the same set, and the number of optical signals that can be transmitted simultaneously can be increased.

Further, according to the present invention, since the second polarization adjusting means for adjusting the polarization plane of the input optical signal so as to be linearly polarized and orthogonal to each other is provided, the polarization of the optical signal in the optical transmission line is provided. Even if the wavefront fluctuates, an optical signal can be received without generating an optical beat. Further, in the present invention, the first measuring means for measuring the state of the polarization plane of the optical signal output to the optical transmission line, and the adjustment of the polarization plane by the first measuring means is controlled in accordance with the measurement result. A first control unit, a second measurement unit for measuring a state of a polarization plane of the optical signal input from the optical transmission line, and a polarization state of the polarization plane by the second measurement unit according to the measurement result. Since the fourth control means for controlling the adjustment is provided, the polarization plane of the optical signal can be automatically adjusted according to the changing state of the polarization plane of the optical signal.

Further, according to the present invention, a detecting means for detecting optical beat noise generated at the time of receiving an optical signal, and an adjustment of the polarization plane by the second polarization adjusting means according to the detected noise level. And a fifth control means for controlling.
The polarization plane of the optical signal can be automatically adjusted according to the level of the optical beat noise. Still further, in the present invention, a wavelength setting means for setting an emission wavelength of the optical signal, and the first polarization adjustment based on a relationship between a coupling angle of a polarization plane of each optical signal and a noise level of beat noise. Second control means for controlling the adjustment of the polarization plane by the device and for setting the polarization plane to an arbitrary state;
Based on the relationship between the noise level of the beat noise and the wavelength interval, controls the setting of the emission wavelength by the wavelength setting means,
The third control means for setting the emission wavelength to an arbitrary interval is provided, so that the adjustment of the polarization plane of the optical signal and the setting of the emission wavelength are arbitrarily controlled to set the level of the optical beat noise to “0”. Can be.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of a system configuration using an optical signal transmission method according to the present invention.

FIG. 2 is a relationship diagram showing a relationship between a coupling angle of a polarization plane of an optical signal and a beat level.

FIG. 3 is a block diagram showing a second embodiment of a system configuration using an optical signal transmission method according to the present invention when three or more optical signals exist.

FIG. 4 is a block diagram showing a third embodiment of the system configuration according to the present invention.

FIG. 5 is a block diagram showing a fourth embodiment of the system configuration according to the present invention.

FIG. 6 is a relationship diagram showing a relationship between a RIN value and a wavelength interval at each beat level.

FIG. 7 is a relationship diagram illustrating a relationship between a beat level and a wavelength interval when a noise value having a RIN value of −130 dB / Hz occurs.

FIG. 8 is a block diagram showing a fifth embodiment of the system configuration according to the present invention.

[Explanation of symbols]

 Reference Signs List 1 center station 2, 13, 23, N3 polarization adjuster 3 light receiver 4 demodulator 5 optical fiber 6 optical coupler 10, 20, N0 terminal station 11, 21, N1 light source 12, 22, N2 modulator 31, 41 polarization Wave analyzer 32, 33, 42, 44 Controller 43 Noise detector

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI H04B 10/04 10/06 (72) Inventor Hideyuki Nasu 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Inside Furukawa Electric Co., Ltd.

Claims (25)

[Claims] 1. An optical signal transmission method in which optical signals output from a plurality of transmitting units are combined and transmitted to an optical transmission line, and the optical signals are received by a light receiving unit and demodulated. An optical signal transmission method comprising: adjusting polarization planes of an optical signal in directions orthogonal to each other; 2. The optical signal transmission method according to claim 1, wherein the transmission unit converts the polarization plane of the optical signal into linearly polarized light and outputs the optical signal orthogonal to each other. 3. The transmitting unit, when there are at least three optical signals, two light emitting wavelengths that are the same or adjacent to each other.
As a set of the two optical signals, the polarization planes of the optical signals of each set are adjusted in directions orthogonal to each other, and the optical signal of the set and another set or 1 in which the optical signal and the emission wavelength of the set are adjacent to each other. 2. The optical signal transmission method according to claim 1, wherein a wavelength interval between the two optical signals is set to a predetermined interval and output. 4. The optical signal transmission method according to claim 3, wherein the transmitting unit converts the polarization plane of each set of optical signals into linearly polarized light and outputs the optical signals orthogonal to each other. 5. The optical signal transmission method according to claim 1, wherein the transmitter adjusts the combined optical signals so that the combined optical signals are orthogonal to each other. 6. An optical signal transmission method in which optical signals output from a plurality of transmitting units are combined and transmitted to an optical transmission line, and the optical signals are received by a light receiving unit and demodulated. Based on the relationship between the coupling angle of the polarization plane of each optical signal and the noise level of the beat noise, the polarization plane of each optical signal is adjusted to an arbitrary state, and based on the relationship between the noise level of the beat noise and the wavelength interval. An optical signal transmission method, wherein the light emission wavelength of each optical signal is set at an arbitrary interval and output. 7. The transmission unit according to claim 1, wherein the transmission unit measures a state of a polarization plane of the combined optical signal, and adjusts a polarization plane of the optical signal according to the measurement result. The optical signal transmission method according to any one of the above. 8. The light according to claim 1, wherein the light receiving unit measures a state of a polarization plane of the input optical signal, and adjusts a polarization plane of the input optical signal according to the measurement result. Signal transmission method. 9. The apparatus according to claim 1, wherein the light receiving unit detects noise generated when the optical signal is received, and adjusts a polarization plane of the input optical signal in accordance with the detected noise level. Item 7. The optical signal transmission method according to item 1 or 6. 10. The light receiving unit according to claim 1, wherein the state of the plane of polarization of the input optical signal is adjusted to the state of the plane of polarization of the optical signal when the transmitting unit outputs, and the light is received. Item 10. The optical signal transmission method according to any one of Items 1, 6 to 9. 11. The optical signal transmission according to claim 1, wherein the light receiving unit receives the input optical signal by adjusting the plane of polarization of the input optical signal to linearly polarized light and adjusting the polarization plane to be orthogonal to each other. Method. 12. An optical signal transmission device that combines optical signals output from a plurality of light sources, transmits the combined optical signals to an optical transmission line, and receives and demodulates the optical signals by a light receiving unit. An optical signal transmission device comprising: first polarization adjusting means for adjusting polarization planes in directions orthogonal to each other. 13. An optical signal transmission device for combining optical signals output from a plurality of light sources and transmitting the combined optical signals to an optical transmission line, receiving the optical signals by a light receiving unit, and demodulating the optical signals. First polarization adjusting means for adjusting polarization planes in directions orthogonal to each other, and changing the state of the polarization plane of the optical signal from the optical transmission line to the first polarization adjustment state.
An optical signal transmission device comprising: a second polarization adjusting unit that adjusts the state of the polarization plane when the polarization adjusting unit adjusts. 14. The apparatus according to claim 12, wherein the first polarization adjusting unit adjusts the plane of polarization of the optical signal from the light source so as to be linearly polarized and orthogonal to each other. Optical signal transmission device. 15. The first polarization adjusting unit, when at least three optical signals are present, sets two optical signals having the same or adjacent light emission wavelengths as a set, and sets each of the optical signals in each set. While the polarization planes are orthogonal to each other, the light source sets the wavelength interval between the set of optical signals and another set or one of the optical signals adjacent to the set of optical signals and the emission wavelength at a predetermined interval. 14. The optical signal transmission device according to claim 12, wherein the optical signal is transmitted. 16. The optical signal transmission according to claim 15, wherein the first polarization adjusting unit converts the polarization plane of each set of optical signals into linearly polarized light and outputs the polarization planes orthogonal to each other. apparatus. 17. The optical signal transmission according to claim 12, wherein the first polarization adjusting unit adjusts the combined optical signals so as to be orthogonal to each other. apparatus. 18. The apparatus according to claim 1, wherein the second polarization adjusting unit converts the polarization plane of the input optical signal into linearly polarized light, and adjusts the polarization plane so as to be orthogonal to each other and receives light.
4. The optical signal transmission device according to 3. 19. The optical signal transmission device, comprising: first measurement means for measuring a state of a polarization plane of an optical signal output to the optical transmission line; and the first polarization adjustment according to the measurement result. 14. The optical signal transmission device according to claim 12, further comprising: first control means for controlling adjustment of the polarization plane by means. 20. An optical signal transmission device that combines optical signals output from a plurality of light sources, transmits the optical signals to an optical transmission line, and receives and demodulates the optical signals by a light receiving unit. First polarization adjusting means for adjusting a state, wavelength setting means for setting an emission wavelength of the optical signal, and a relationship between a coupling angle of a polarization plane of each optical signal and a noise level of beat noise, Second control means for controlling the adjustment of the polarization plane by the first polarization adjustment means to set the polarization plane to an arbitrary state; and setting the wavelength based on the relationship between the noise level of the beat noise and the wavelength interval. Controlling the setting of the emission wavelength by the means,
An optical signal transmission device, comprising: third control means for setting the emission wavelength to an arbitrary interval. 21. An optical signal transmission device that combines optical signals output from a plurality of light sources, transmits the optical signals to an optical transmission line, receives the optical signals at a light receiving unit, and demodulates the optical signals. First polarization adjusting means for adjusting a state, wavelength setting means for setting an emission wavelength of the optical signal, and a relationship between a coupling angle of a polarization plane of each optical signal and a noise level of beat noise, Second control means for controlling the adjustment of the polarization plane by the first polarization adjustment means to set the polarization plane to an arbitrary state; and setting the wavelength based on the relationship between the noise level of the beat noise and the wavelength interval. Controlling the setting of the emission wavelength by the means,
Third control means for setting the emission wavelength to an arbitrary interval, and changing the state of the polarization plane of the optical signal from the optical transmission line to the first
An optical signal transmission device comprising: a second polarization adjusting unit that adjusts the state of the polarization plane of the optical signal when the polarization adjusting unit adjusts. 22. The optical signal transmission device includes first measurement means for measuring a state of a polarization plane of an optical signal output to the optical transmission line, and the second control means includes a measurement result and a measurement result. 22. The polarization plane adjustment by the first polarization adjustment unit is controlled based on the relationship between the coupling angle of the polarization plane of each optical signal and the noise level of beat noise. Optical signal transmission equipment. 23. The optical signal transmission device according to claim 2, wherein said optical signal transmission device measures a state of a polarization plane of said optical signal input from said optical transmission line.
23. A measurement device according to claim 13, further comprising: a fourth control device configured to control adjustment of the polarization plane by the second polarization adjustment device according to the measurement result.
The optical signal transmission device according to any one of the above. 24. The optical signal transmission device, comprising: detecting means for detecting noise generated when the optical signal is received, and the polarization plane by the second polarization adjusting means according to the detected noise level. 24. The optical signal transmission device according to claim 13, further comprising: fifth control means for controlling the adjustment of the optical signal. 25. The optical signal transmission device according to claim 12, wherein the optical transmission line is made of a polarization maintaining fiber.